The picture probably showed up in one of your feeds. It fit all sorts of algorithmic criteria for viral interestingness, shapes and colors and scale otherwise unseen in nature: The steep bank of a Montana river littered with the bare fuselages of three Boeing airplanes spilled from a train track above like oversized logs swathed in aquamarine-colored protective wrap. Or maybe not logs, but uniformly skinny whales beached far from any ocean. Either way, an eye-grabbingly irresistible curiosity. In the foreground, always, whitewater rafters taking selfies.

The river is called the Clark Fork. And I’ve paddled that stretch in canoes and rafts with some of the rafters who showed up in some of those pictures. It’s a section about 40 freeway minutes downstream of Missoula called Alberton Gorge, named for nearby Alberton, Montana—an off-Interstate mountain town of four or five hundred people. Within roughly seven easily accessible river miles are five major rapids that, depending on the flow, range from Class II to Class IV. The last of these is called Fang, and it was just downstream of Fang that the planes were tossed down the bank, coming to scattered rest with their snouts or tails in the water.

The Gorge is a fun stretch to run, but it makes you pay attention. While drownings are infrequent, substantial injuries are hardly unheard of. Boats are flipped all the time in Alberton Gorge, spilling bodies and gear that is later recovered or washed downstream to the intake grates of the next dam, at Thompson Falls, and trucked off to a landfill.

You wouldn’t know it from rocky Alberton Gorge, which is host to an almost constant stream of kayakers and rafters during the temperate months, but the Clark Fork is one of the most badly abused rivers in the United States, and simultaneously one of the luckiest.

The Clark Fork was a victim of copper mining. That industry’s needs and wastes pretty much killed the river’s upper 120 miles for the better part of 100 years. But over the last several decades, and especially the last several years, by way of a dam removal and landscape-scale restoration engineering, the river has been largely restored to a semblance of ecological and hydrological health that hasn’t been seen in a century.

As with most rivers, especially those with an urban component (as in Missoula), strange things get fished out of the Clark Fork all the time. Too often it’s the bodies of homeless men who’ve died under uncertain circumstances. Not infrequently it’s a vehicle that’s been run off a road, icy or otherwise, by a driver, drunk or otherwise. Sometimes it’s airplane fuselages—in this case, being shipped from a fabrication plant in Kansas to Boeing facilities in Washington State for finishing.

Just upstream of Missoula, it was 500,000 cubic yards of river sediment piled up behind the Milltown dam—part of a Superfund-designated environmental disaster stretching 120 river miles. The sediments were contaminated to the point of toxicity by copper mining and smelting byproducts including arsenic, mostly, but also nickel, cadmium, and lead. It took two years to dig it all out of the lake bed behind the dam and load it onto trains and deliver it 100 miles upstream to the BP/ARCO Waste Repository—aka the “Opportunity Ponds”—bordering the hamlet of Opportunity, Montana. There it joined some six square miles of mine tailings already deposited there over the course of a century of waste-intensive mining operations in the area—an area of longstanding but now-defunct importance to the global copper industry, and the wellspring of several great American fortunes. BP/ARCO repository is on the hook to manage the Opportunity area in perpetuity—however long that might turn out to last—to keep these stored sediments out of the river forevermore.

I took Opportunity’s name for the title of my book because I was fascinated by the way that tiny community had been sacrificed twice: first, by the copper industry, as a deceitfully named dumping ground; more recently by the celebrated environmental victory that sparked the Clark Fork’s restoration. Neither could have been accomplished without someplace to dump the spoil.

But Opportunity, Montana is as much about the Clark Fork as it is about that small community on its banks. It’s a river that starts as a rivulet, becomes a municipal storm drain, and threads through engineered meanders on its way toward Alberton Gorge. Near Warm Springs, the river is stalled out in a series of settling ponds and dosed with lime to reduce its acidity. Near Opportunity, it’s been dug up and reconstructed from scratch. In Missoula, it flows over boulders cemented into the riverbed to create play waves for kayakers.

Long stretches of the Clark Fork have been shunted into culvert pipes and routed around deposits of poison sediment 20 feet deep—most of which have by now been dug up and shipped, with the rest of the mess, to Opportunity. That poisoned earth has been replaced with “donor soil” poached from sparse local supplies and given riverine shape by matted tubes and carefully scattered stone and planted with native vegetation. After a couple of years the results look surprisingly good, almost natural. There are occasional blowouts—there have been since the 1908 flood that caused the lion’s share of the Clark Fork’s damage—but they seem to be more and more contained as the river rediscovers its way.

But as the pictures splashed across Facebook showed, there will always be spills. Derailments in this western part of the state are relatively common. Usually it’s something inert and, while expensive, not particularly damaging, like the fuselage of a plane. Sometimes, as in a 1996 derailment spill near Alberton, it’s chlorine and potassium cresylate. In the future, some Clark Fork watchers fear, it could be a string of coal cars, or tankers carrying crude from the Bakken shale play in eastern Montana.

One such difficulty has recently become an issue just upstream at the site of the former Smurfit-Stone paper mill near Missoula, which is currently under consideration for Superfund designation due to the metals, dioxins, and chlorinated organic compounds found in the defunct mill’s storage ponds. And it was long an issue at Milltown dam upstream of Missoula. It remains an issue farther upstream at the Clark Fork’s jumbled source, in the elevated outskirts of Butte, Montana, where an astounding pile of metals-laden slurry sits behind a bulldozer-built dam of contaminated dirt called the Yankee Doodle tailings.

The Yankee Doodle tailings are enormous: a thousand acre tailings pond held in place by a 600-foot earthen dam. Released by, say, a catastrophic weather event or an earthquake, the Yankee Doodle wastes could essentially undo more than a billion dollars of investment already poured into in the Clark Fork’s restoration.

One doesn’t mean to be unduly alarmist, but perpetuity is a long time. Accidents happen, and anyone who wishes to avoid their worst consequences should probably expect history to repeat itself. The history of the Clark Fork is a history of things being dumped—by accident and by design—in a river where they don’t belong.

By Wednesday, six days after the derailment, the last of the Boeing fuselages had been removed from the river by crews working for Montana Rail Link—the freight line responsible for the spill, and the same railroad, coincidentally, that for two years ferried the Milltown dam sediments upstream to the dumping grounds at Opportunity. Some spills are harder to clean up than others.

Unlike the small stream that borders Opportunity, the Clark Fork running through Alberton Gorge is in the process of becoming a big river, having already taken on most of the hundreds of tributaries that make it the state’s biggest river by volume.

It’s been big enough to absorb a lot of abuse over the years, and the temporary intrusion of a few aluminum airplane bodies isn’t likely to do any lasting harm. But their brief, incongruous presence should serve as more than an odd photo op. It should be a reminder that accidents are likely, if not in fact inevitable, and that when it comes to keeping rivers clean of unwanted intrusions—like, for instance, the millions of tons of toxic sediments currently corralled atop the Clark Fork’s headwaters—we can hardly be too cautious.

The picture probably showed up in one of your feeds. It fit all sorts of algorithmic criteria for viral interestingness, shapes and colors and scale otherwise unseen in nature: The steep bank of a Montana river littered with the bare fuselages of three Boeing airplanes spilled from a train track above like oversized logs swathed in aquamarine-colored protective wrap. Or maybe not logs, but uniformly skinny whales beached far from any ocean. Either way, an eye-grabbingly irresistible curiosity. In the foreground, always, whitewater rafters taking selfies.

The river is called the Clark Fork. And I’ve paddled that stretch in canoes and rafts with some of the rafters who showed up in some of those pictures. It’s a section about 40 freeway minutes downstream of Missoula called Alberton Gorge, named for nearby Alberton, Montana—an off-Interstate mountain town of four or five hundred people. Within roughly seven easily accessible river miles are five major rapids that, depending on the flow, range from Class II to Class IV. The last of these is called Fang, and it was just downstream of Fang that the planes were tossed down the bank, coming to scattered rest with their snouts or tails in the water.

The Gorge is a fun stretch to run, but it makes you pay attention. While drownings are infrequent, substantial injuries are hardly unheard of. Boats are flipped all the time in Alberton Gorge, spilling bodies and gear that is later recovered or washed downstream to the intake grates of the next dam, at Thompson Falls, and trucked off to a landfill.

You wouldn’t know it from rocky Alberton Gorge, which is host to an almost constant stream of kayakers and rafters during the temperate months, but the Clark Fork is one of the most badly abused rivers in the United States, and simultaneously one of the luckiest.